The accuracy of accelerometers for inertial navigation purposes have long been limited by the accuracy of the proof-mass suspension. Earlier designs have sought to eliminate some of these limitations by the use of flotation fluid to partly or totally eliminate mechanical forces acting upon the proof-mass suspension. Although successful in the stated purpose, such accelerometers are very difficult to produce and hence prohibitively expensive. Most accelerometers produced today are of the air-filled type. In these kinds of accelerometers, the flexure suspension must maintain a high spring rate against movements that do not coincide with their input or sensitive axis. In order to give these kind of accelerometers the desired degree of accuracy, their pendulous mass must be made relatively high. In addition, it is necessary to permit relatively large deflections of the proof-mass in order to either guarantee a high shock capability or "memory" in nuclear hardened systems where a temporary loss in electrical functions result during a high flux exposure. The requirements thus stated results in a flexure suspension, where the stress levels are quite high.
Cold working from the machining operations together with the high operating stress combine to make the accelerometer flexure show considerable hysteresis and bias instability effects. Often hysteresis effects of several parts per thousand can be encountered, even in the most careful of designs. In order to still be able to manufacture accelerometers, other parameters must be compromised such as stop freedom about the input axis or the flexure must be made excessively weak in the direction of the input axis.
Splat cooling is a process in which a material is rapidly cooled so that it solidifies in an unorderly atomic form.
The advent of splat cooling makes it possible to create many heretofore unknown materials with unique properties. It has been known for some years that it is practical to manufacture such materials where the cooling is made rapidly in the order of 10.sup.6 C. degrees per second, that metals solidify without an orderly atomic structure. These materials like glass are amorphous. One material commercially available from Allied Chemical is called Metglas. From an instrument standpoint this material is interesting because it lacks grain boundaries where energy absorption and thus hystereis and bias instability in conventional metals occur. The strength of metallic glass is also astonishing. It is about four times as strong as the most common accelerometer flexure material.
Up to this point, it has not been feasible to utilize these outstanding properties in an accelerometer flexure because cooling requirements are difficult to meet in order to produce metallic glass. Second, it is difficult to utilize metallic glass in strip form in accelerometer flexures because of problems in anchoring the metallic glass to the rest of the accelerometer structure as would be required in a "taut band" suspension, for instance.